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Homework Help: Half equations

  1. Mar 25, 2008 #1
    The thermite process can be used to weld lengths of railway track together. A mould placed over the ends of the rails to be joined is filled with a charge of aluminium powder and iron(iii) oxide. When the mixture is ignited, a redox reaction occurs to form molten iron, which joins the rails together.

    a. Write a half equation for the conversion of iron(iii) oxide to metallic iron.

    i got Fe2O3 + 6H+ +6e- = 2Fe + 3H20- but thats wrong according to the book, the answer is Fe2O3(s) + 6e- --> 2Fe(l) + 3O 2- (s). I don't understand why they balanced it using oxygen instead of water.

    b. Write the overall equation for the thermite process.
     
  2. jcsd
  3. Mar 26, 2008 #2

    chemisttree

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    Because that would be two half reactions...

    6H+ + 3O-2 ------> 3H2O

    and

    Fe2O3 + 6e- -------------> 2Fe(0) + 3O-2
     
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